Calender bank size indicator



Aug. 9, 1966 J. T. FREEMAN 3,264,682

CALENDER BANK SIZE INDICATOR Filed Jan. 2, 1964 5 Sheets-Sheet 1 INVENTOR JOHN THOMAS FREEMAN BY 74% a M,Q.

AGENT Aug. 9; 1966 J T. FREEMAN CALENDER BANK S I ZE I ND I OATOR Filed Jan. 2, 1964 FIG.

5 Sheets-Sheet 2 INVENTOR JOHN THOMAS FREEMAN AGENT Aug. 9, 1966 Filed Jah. 2, 1964 J. T. FREEMAN CALENDER BANK SIZE INDICATOR 3 Sheets-Sheet 3 CURRENT SUPPLY INVENTOR JOHN THOMAS FREEMAN AGENT United States Patent 3,264,682 CALENDER BANK SIZE INDICATOR John Thomas Freeman, Freehold, Nl, assignor to E. I.

du Pont de Nemours and Company, Wilmington, DeL,

a corporation of Delaware Filed Jan. 2, 1964, Ser. No. 335,218 4 Claims. (Cl. 18-2) This invention relates to quality control applicable for use in calendering operations. More particularly it relates to an apparatus for determining the size of a bank in the nip between two calender rolls.

In the formation of some viscous products by a calendering operation it is important that the final product be free from air bubbles. This is particularly true in the manufacture of sheet or webs of photopolymer. The method of the invention will be illustrated and described in connection with the manufacture of photopolymerizable compositions and elements such as disclosed in assignees US. patents, Plambeck US. 2,760,863 and 2,791,504; Barney US. 2,893,868; Martin US. 2,902,365; Martin et al. U.S. 2,927,022; and Smith US. 3,012,952. It should be understood that such illustrations and descriptions are merely exemplary in that the invention may be adapted with little or no modification to other calendering operations where the quality of the final product is related to bank size.

In the manufacture of photopolymerizable compositions it has been found that there is a close relationship between the size of the calender bank and the incidence of bubbles. The feed involved in the calendering of photopolymer is in the form of small particles or chips. During the pass of the feed through the first nip in the calendering operation, many small pockets of air are 'trapped in the web created. These air pockets will be worked out of the web as they revolve in properly sized banks in the subsequent nips in the calender.

'banks involved are too small, they will tear and trap addi- If the tional air which will be found in the final product as bubbles. Additionally it has been found that if the bank size is too large, layers known in the art as pancakes will form on the surface of the bank. The pancakes can not be used and must be removed, usually by hand. Therefore, it is desirable to obtain and maintain the optimum bank size for the material being calendered.

The prior method of gauging bank Size was by the direct visual observation or indirect observation via television by a trained operator. The operator upon observing the bank and determining that the size was either too r small or large would either increase or decrease the size 'of the initial nip to regulate the flow of polymer or he would adjust the feed rate to obtain the desired bank size.

This method has many drawbacks, and one is that it requires the attention of a skilled operator.

In many photopolymer calendering operations the diameter of the part of the bank that can be observed is between A and -78", and even with skilled operators the changes in bank size that will effect the formation of bubbles are very slight and in many instances cannot be detected by visual Y observation.

Other objects will appear hereinafter.

' third 16 nips.

3,264,682 Patented August 9, 1966 ice It has been found that these and other important objects and advantages are accomplished in accordance with this invention which is particularly pointed out in the appended claims.

The invention is best explained by means of the attached drawings and the following discussion describing the preferred embodiments; however, this invention is not limited to these embodiments except as disclosed in the appended claims.

FIG. 1 is a side elevation of a calendering operation;

FIG. 2 is a partially cut-away view of the preferred apparatus for carrying out the method of the invention;

FIG. 3 is a suitable electrical circuit for the preferred apparatus;

FIG. 4 represents an automatic system utilizing this invention.

Referring now to FIG. 1, the charge 11 is fed into the first nip 12 between calender rolls 1 and 2. The charge is transported to the calender by a conveyor 13. After the charge passes through the first nip it assumes the form of a film or web 14. This web then passes through two successive nips 15 and 16 wherein it is further mixed and reduced to the prescribed gauge. Transfer from one roll to the next is familiar to those skilled in the art and is generally accomplished by combinations of temperature, speed, or surface-finish differential. The Web is then stripped by a smaller roller 17 and is then ready for further processing.

In the illustrated inclined calender the number 3 roll is fixed and rotates in the direction shown. The other three rolls are movable in the directions indicated, this allows the size of the three nips through which the web passes to be adjusted. Additionally the rolls may be skewed, i.e., the axis of one roll slightly rotated out of the plane of the other. This increases the nip opening at the ends of the rolls relative to that at the center and compensates for the deflection of the rolls.

In the second 15 and third 16 nips the flow properties of the material in the charge and the size of the nip result in a buildup 18 of the material all along the length of the nip. This buildup is called the calender bank or cigar by those familiar with the art. The banks are classified as either folding banks or rotating banks depending upon the flow properites of the material involved. In the manufacture of photopolymerizable elements the bank that is formed is a rotating bank and the bank usually extends most of the length of the nip. The size of the bank may be uniform along the whole length of the nip or it may be largest at the center and taper in size toward the nip ends.

In the manufacture of photopolymer it is the size of the revolving banks 18 that must be controlled to prevent the formation of bubbles and pancakes. In the illustrated embodiment the bank size is being measured by the apparatus of the invention 19 at the second 15 and In some calendering operations it will be sufiicient to measure the bank size at only one nip, i.e., the one closest to the initial nip of the calender, for the required quality control.

FIGURE 2 is a detail of the apparatus used to carry out this invention. Basically the apparatus employs a rollerlike probe 20 that rides on the surface of the revolving bank near its center. The roller is mechanically linked to a soft iron core 21 that moves within a differential transformer 22 such that a change in bank size results in a proportional change in the voltage induced in the transformer.

More particularly a free running roller 20 made of a plastic-like material such as tetrafluorethylene resin or nylon is mounted on a nylon axle. A roller made of tetrafiuorethylene resin is preferred in the calendering of photopolymer since such a roller does not stick to the polymer, thus lessening the chances of being drawn into the nip. The size of the roller is not critical; the only requirement is that it is small enough to fit within the. nip

and ride on the surface of the bank. The roller is inserted in a slot on the tapered end of a feeler or plunger 23 with the axle being placed in holes in the sides of the slot and fixed in place.

While the angular placement of the plunger and the attached roller with respect to the bank and the nip is not critical, it has been found that if they are placed slightly above the center line of the nip the possibilities of=the assembly being drawn into the nip is greatly reduced. The center line of the nip being a line through the center of the nip located equidistantzfrom the two rollers and parallel to tangents drawn from the rollers 'at their closest point of convergence. Additionally as can be observed in FIG. 1, the plunger23 during operation is located at an angle ofapproximately 30 from the horizontal; thereby the force of gravity keeps the roller in contact with the revolving bank.

The plunger can be made of many plastic-like materials, such as nylon, polytetrafluorethylene, or assignees Delrinacetal resin. The other end of the cylindrical plunger has a smooth sliding fit in a hole reamed in one end of a nonmagnetic housing 24, such as a housing made of bronze, brass or Delrin acetal resin. screw is threaded into a hole tapped in the housing and it extends into a milled keyseat 26 in the plunger.-

The screw and keyseat coact to control the extent of the movement of the plunger and keep it from leaving the hole in the housing.

A nylon rod 27 has a snug fit in a hole drilled into the inserted'end of the plunger. This rod passes through a reamed hole 28 in the housing and threaded on its other end is a soft iron core 21., This core is moved by the action of the plunger between-the magnetic field ofthe differential transformer 22 and a hole 29 reamed in the housing. The smaller diameter of the hole 28"reamed for the rod 27 limits the motion of the core.

Thus the roller 20 moves on the surface of the revolv-- ing bank, and any size change in the bank results in a.

proportional movement of the plunger 23, nylon rod 27 and steel core 21. The movement of the core within the magnetic field of the difierential transformer creates a,

signal by means that willbe explained later.

A shear pin 30 is inserted in a hole drilled through the plunger and rod. The hole in plunger 23 represents a weak point at which the plunger is easily broken. Inthe event the roller is drawn into the nip of the calender,

the plunger and rod will break at this point due to the. stress created between the opposite pulling of =the.sup-.

port and calender rolls. This insures that onlylthe relatively small nylon and tetrafluorethylene resin components will pass through the nip. They can be crushed by the rolls and decrease the possibility of damage to the calender rollsurface. Any plunger material can be used which. is easily crushed by the rolls and any connecting means can be employed that will easily disengage the plunger when it is caught.

The housing 24hasa smooth sliding fit one. metal slide 31. The slide has steps 32 and 33 at each end and.

an adjusting rod 34 is inserted through a hole in one -.of the stops 33 and threaded into a tapped hole in the hous ving. Movementof adjusting nuts 35 will move the housing over the length of the .slide. This adjustmentwill allow the loc'ationof the plunger to be varied when a large. change in bank sizeis created by changing the desired gauge of the web.

The slide is fastened to a bracket 36'by the use of inachine screws 37.. Onto this bracket is welded a wheel bracket 38 that holds a shaft 39*connected to two wheels 40. These wheels ride on the surface of the calender roll'andhelp support the housing and sensing :unit.

T0 provide lateral support another bracket 41 can be.

A machine connectedto the wheel bracketassernbly by machine, screws 42.. This bracket can then be'connected toa support (not shown) that extendsjthe length of the calender .rolls and is mounted on'the calender frame (not 7 shown).

The differential transformer 22 consists, as disclosed in US. Patents 2,050,629 and 2,427,866, essentially. of a primary coil 43, two secondarycoils 44 and 45, and the core 21'of magnetic material; The primary coil is ener-. gized from a suitable source-of alternating current by electrical conduits (not shown). The two secondary coils 1 communicate with electrical conduits 46 and 47 andwith each other by means of conduit 48 isothat their output voltages induced ,in these secondary .coils will be equal and out. of phase .and a theoreticaloutput of zero will result. .This condition denotes the .null orbalance point of .the differential transformer. the core caused by movement of the roller 20=will cause Hence movement of 2 a generation of voltage proportional to the amount of movement.- And-since movement in this case is substan- 1 tially proportional to :the bank size, one; can .obtainan;

indication 30f the bank size almost directly from the voltage.

FIGURE 3 indicates a suitable 'electricaLcircuit for theapparatus of the invention. A stepdown transformer 49 reduces the normaliline voltage .to onethatis compatible with {the differential transformer =22 used. When 1 using a 6.3 volt input differentialtransformer such as that manufactured by Schaevitz Inc., Pennsauken, New'lersey, the stepdown transformer shouldreduce the line voltage i to around five .volts.. A variable resistance- 52 may beused to reducethe input to the. differential transformer to approximately one volt, this. gives the recording-DC.

voltmeter 51a greater span. The output of the, dilferential transformer 22is transmitted .to an AC. to DLC. silicon diodehalfwave rectifier 50 and then to a D.C..voltages recorder. such as made. by Honeywell may-be used.

recorder '51.. A. 0 to 1 millivolt voltmeter with astrip The'indu'ced voltage is representative of bank size and after being recorded can be used directlyor indirectly for controlling the calender bank size.., An operator upon observing the bank size from the recorder could v; manually adjust the size of the hips or the rate; of feed to control the=bank size.- Ifi desired, the electricalsignal.

representing the :bank size could be transduced into. a r

pneumatic signal.

of the calender; If an automaticcontrol system is used,

control;

An automatic system utilizing this'delvice is disclosed I in assignees application of Freeman and Sanders. entitled 5 Apparatus and Processfiled Ja'nuaryj2,'1964, Serial i No. 335,220. This system is briefly disclosed byFIG..4 I where the electrical signal produced'by the sensing device.

the voltages used in FIGURE 3 will have to be increased 5 as they are suflicient for recording purposes: but not for 19 is an AC. signal: and has a magnitude that varies, as 1 a function of the size ofthe bankl This signal is convertedinto a DC..signa1 having :a vIangeof 0 -50. mv. by

an A.C./D.C. rectifier 53. The output of the rectifier can be recorded on recorder 54..

The DC. signal from the rectifier is transmitted to an electrical/ pneumatic transducer 55. This transducer produces a proportional pneumatic output signal in the range of 3 to p.s.i. dependent upon the strength of the DC. input.

The pneumatic signal from the transducer is sent to a proportional plus reset pneumatic controller 56. This controller first, compares the pneumatic signal representing the measured bank size or primary feedback with a reference pneumatic signal. The reference signal is a manually set signal entering the controller through valve 57 which represents the desired or optimum bank size. Then if there is any difference between the two signals, the difference is amplified within the controller. Thus for a given deviation from the optimum set point, the controller output contains the deviation times a factor dependent upon the gain setting of the controller. Prior to leaving the controller the output signal is integrated with respect to time by the action of the reset-rate needle valve. A controller that can be used is the Moore Products Nullmatic, Model 56M.

The controller output signal is transmitted to a Bailey roll positioner 58. This device compares the controller output signal with a force that represents the angular position or rotation of the shaft of the means that moves one of the calender rolls, i.e., one of the rollers that determined the nip size. In other words, this force represents the shaft position of the nip motor which in turn is representative of nip size. The difference between the two inputs to the positioner is used to operate one of the two pressure switches 59 that are in the electrical circuit that supplies the power to the roll positioning motor 60.

Thus if the angular position of the shaft is correct for the bank size desired, the output of the positioner will not operate either of the pressure switches and the nip or roll positioning motor will not be activated. If the output indicates an error in the shaft position, depending on whether the calender rolls are too far apart or too close one of the pressure switches will close and the nip motors will run either in or out to correct the error. The rotation of shaft 61 is imparted to gear box 62 which in turn causes the movement of the calender rolls.

The roll positioner 58 is sensitive to angular movement of shaft 61 and a coupling means 63 is employed between the positioner and shaft to provide for initial operational adjustments between the shaft and positioner and to reduce error caused by friction, etc. Suitable coupling means that can be used is a differential drive unit or an electric slip coupling type FFK60 manufactured by Simplatrol Products Corp.

The operation of the entire control unit may be cycled with respect to the operation of the calendering unit. The power input to the roll positioning motor to motor 60 is transmitted through a manually set proportional timer 64 and the nip motors are only activated for a portion of the time the unit is in operation, e.g., the automatic control unit can be in operation for of a sec. basic cycle for which the timer is pro-set.

The operation of the invention has been illustrated by the use of a feeler type sensing device in conjunction with a differential transformer whereby the feeler is in physical contact with the bank. Other means that continually and accurately sense the bank size and develop a signal proportional to the bank size may be used without departing from the spirit of the invention. In the applica tion involving photopolymer the physical contact between the feeler and bank does not damage the final web, but if such contact would damage the web other means could be used. The size of the bank could be sensed by an air gauge, ultraviolet radiation, nuclear radiation, sound absorption, or dielectric absorption and a corresponding signal developed.

This invention has the advantage over the visual system of bank size control in that it greatly multiplies the change in size, making it instantly apparent when a small change in bank size has occurred. Another advantage of the invention is that it provides a necessary tool to find the optimum bank size to close dimensions for any material being calendered. The invention also has the advantage of supplying a usable output for the pneumatic control of the bank size.

What is claimed is:

1. In combination with calender rolls for calendering viscous material into sheet form a detecting device for measuring calender bank size comprising (A) supporting means for holding said detector in operational position adjacent the nip between two calender rolls,

(B) sensing means mounted on said support means for continuously determining said bank size, and

(C) means for converting said bank size determinations into a signal that varies as a function of the bank size.

2. In combination with calender rolls for calendering viscous material into sheet form a detector device for measuring bank size comprising (A) supporting means for holding said detector in operational position;

(B) a differential transformer connected to said support; and

(C) feeler means connected to the core of said transformer for transmitting variations in said bank size to said transformer.

3. An apparatus as defined in claim 2 where said differential transformer (B) has a soft iron core on a rod; said converting means (C) is a feeler that contacts said bank; and where there is also provided shearable connecting means (D) for connecting said core rod to said feeler.

4. An apparatus as defined in claim 3 where said feeler (C) comprises a plunger with roller means at one end to contact the surface of said bank and said shearable connecting means comprises a shear pin located in a hole drilled through said rod and plunger whereby said rod and plunger is weakened at this point to snap under excessive stress created by pulling said plunger.

References Cited by the Examiner UNITED STATES PATENTS 2,809,519 10/ 1957 Kaestner 73-159 2,858,614 11/1958 Schuenemann 33-148 3,149,421 9/1964 OBrien 33-172 3,193,937 7/1965 Aller 33-169 ROBERT F. WHITE, Primary Examiner.

S. A. HELLER, Assistant Examiner. 

1. IN COMBINATION WITH CALENDER ROLLS FOR CALENDERING VISCOUS MATERIAL INTO SHEET FORM A DETECTING DEVICE FOR MEASURING CALENDER BANK SIZE FOR COMPRISING (A) SUPPORTING MEANS FOR HOLDING SAID DETECTOR IN OPERATIONAL POSITION ADJACENT THE NIP BETWEEN TWO CALENDER ROLLS, (B) SENSING MEANS MOUNTED ON SAID SUPPORT MEANS FOR CONTINUOUSLY DETERMINING SAID BANK SIZE, AND (C) MEANS FOR CONVERTING SAID BANK SIZE DETERMINATIONS INTO A SIGNAL THAT VARIES AS A FUNCTION OF THE BANK SIZE. 